In a conventional turbofan gas turbine engine a fan, compressor, high pressure turbine (HPT), and low pressure turbine (LPT) are disposed in serial flow communication. The HPT extracts energy from combustion gases flowing therethrough to power the compressor, and the LPT further extracts energy from the combustion gases for powering the fan. A conventional LPT includes a plurality of axial stages of stator vanes extending radially inwardly from a casing and rotor blades extending radially outwardly from rotor discs. The casing is typically split along a horizontal centerline plane for forming two 180.degree. half casings which allow for relatively simple manufacture of the component parts and assembly thereof over the rotor blades and discs. However, this arrangement results in two horizontal flanges spaced 180.degree. apart on each of the half casings, respective ones of which are bolted together during assembly of the LPT. The horizontal flanges, therefore, result in a non-uniform stator casing which during operation of the LPT result in generally elliptical distortion of the casing due to differential temperatures in the casing and pressure loads therein. Since conventional shrouds are attached to the casing and spaced relatively close to the blade tips, any circumferential distortion of the casing affects the shroud-to-blade tip clearance, and therefore, affects LPT performance. As blade tip clearance increases, performance of the LPT decreases.
Also in a conventional LPT, the turbine rotor is formed from several independent rotor discs which include flanges for being bolted together in the LPT. In this way, the conventional dovetail slots in the disc perimeters, either circumferentially extending or axially extending, may be formed independently for each disc and prior to assembly of the several discs. However, manufacturing tolerances of the several rotor discs necessarily require rotor balancing of the entire rotor assembly. Furthermore, the rotor discs are typically bolted together, and during operation of the LPT, relative movement between adjacent rotor discs due to potential slippage at the bolts may result in a degree of unbalance of the rotor during operation which may lead to engine vibration.